Generation of Nanosized Particles during Mechanical Alloying and Their Evolution through the Hot Extrusion Process in Bismuth-Telluride-Based Alloys

Abstract

Our extensive studies of extruded alloys have shown that mechanically strong polycrystalline alloys also deliver surprisingly high thermoelectric performance with ZT > 1 for p-type material in the temperature range from 25°C to 90°C, which was traditionally attributed to the strong texture generated by the extrusion process. Optical and low-resolution scanning electron microscopy observations of the powder produced by mechanical alloying show a particle size distribution in the micrometric range. However, high-resolution transmission electron microscopy (HRTEM) observations of the powders obtained after milling clearly show nanosized crystal grains. The larger microparticles appear to be agglomerations of grains whose size goes down to 5 nm to 20 nm. Examination of bulk n-type and p-type materials using x-ray diffraction (XRD) combined with HRTEM shows that nanosized subgrains can also be found in materials after hot extrusion. In this article we present experimental evidence of the generation and evolution of nanocrystalline particles through the mechanical alloying and hot extrusion processes used to produce the thermoelectric alloys. We also discuss the possible influence of nanocrystalline inclusions on the thermoelectric performance of the produced material. The optimization of the hot extrusion process, in order to maximize the influence of the nanostructures, offers new opportunities to increase the thermoelectric performance of bulk materials.

Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution

“…The correspondent maximum value ZT=1.12 takes place at the temperatures ~ 350÷375 K. The same maximum efficiency ZT=1.1 in the same nanostructured material at the same temperature was measured in Ref. (Vasilevskiy et al, 2010) but the extrusion instead of hot pressing for consolidation of samples was used here.…”

“…The comparison with the experimental data from Sec.2.6 and Ref. (Poudel et al, 2008;Bulat et al, 2010b;Vasilevskiy et al, 2010) showed that the increase of the figure of merit in these materials is hardly connected with the tunneling effect because of the large difference between measured electrical conductivity (of the order of …”

“…An example of such technology is fabrication of bulk nanostructured thermoelectric samples by ball milling of initial materials with subsequent hot pressing (Poudel et al, 2008;Bublik et al, 2009;Bulat et al, 2008aBulat et al, , 2008bBulat et al, , 2009Bulat et al, , 2011bMinnich et al, 2009;Lan et al, 2010), spark plasma sintering (Bublik et al, 2010a or extrusion (Vasilevskiy et al, 2010). In Ref.…”

Structural and Electrical Properties Characterization of Sb1.52Bi0.48Te3.0 Melt-Spun Ribbons

“…Polycrystals are traditionally fabricated using the zone melting method, powder metallurgy techniques or mechanical alloying, followed by a consolidation step [26][27][28][29][30][31]. The melt-spinning (MS) method, based on rapid solidification of the melt that allows attaining cooling rates as high as 10 4 -10 7 K s −1 , has been used to produce these materials by Soviet Union and Russian research groups [32][33][34][35].…”

Термоэлектрические Материалы Для Различных Температурных Уровней

“…Для материала n-типа проводимости пока не получено (ZT ) max > 1 [12][13][14][15][16] (см. таблицу), хотя проводили леги-рование и использовали различные методы получения образцов.…”